Field of the Invention
The present invention relates to an image pickup apparatus having a function of generating a simulation image of, for example, trails of stars, a control method therefor, and a storage medium.
Description of the Related Art
Apparatuses such as compact digital cameras mounted with shooting modes such as a mode in which a star-filled night sky is shot, a mode in which a starry sky and persons are finely shot, and a mode in which diurnal motions of stars are shot as trails to enable easy shooting of the starry sky are sold commercially. Here, when the diurnal motions of the stars are shot as the trails, generally, shooting is repetitively performed under long-time exposure, and the lighten composition of shot frame images is performed. However, the diurnal motions of the stars are very slow, long-time shooting is necessary to shoot the diurnal motions of the stars as the trails, and a user (photographer) does not often know what kinds of trails are shot until shooting is completed. For this reason, determination of a composition before shooting is not easy. Therefore, an image pickup apparatus that predicts positions of heavenly bodies after passage of any time by calculating a position relation of a direction of the image pickup apparatus and the heavenly bodies using information of a GPS sensor and an elevation angle sensor and performs superposition display on a live view image is suggested (refer to Japanese Laid-Open Patent Publication (kokai) No. 2012-4763).
Meanwhile, in a digital camera, an increase in a temperature of an image pickup device due to long-time exposure causes fixed pattern noise such as defects and dark shading to occur. As a result, an image quality may be degraded. In shooting of the trails of the diurnal motions of the stars, because it is necessary to continuously perform shooting under the long-time exposure for a long time, conditions where the fixed pattern noise is easy to occur are met. Therefore, technology for enabling generation of a high-quality image with little fixed pattern noise, even when shooting is repetitively performed under the long-time exposure, is suggested (refer to Japanese Laid-Open Patent Publication (kokai) No. 2015-35717). In the image pickup apparatus described in Japanese Laid-Open Patent Publication (kokai) No. 2015-35717, a black image (light shielding image) is shot individually before and after actual shooting and a noise reduction process is executed using the shot black images.
However, in the image pickup apparatus described in Japanese Laid-Open Patent Publication (kokai) No. 2012-4763, because the GPS sensor, the elevation angle sensor and the like are necessary, a size of the image pickup apparatus may increase and a product cost may increase as well. In addition, in the image pickup apparatus described in Japanese Laid-Open Patent Publication (kokai) No. 2012-4763, only the positions of the heavenly bodies after passage of any time can be displayed and it is impossible to know how the trails of the heavenly bodies are shot. For this problem, a countermeasure to detect the heavenly bodies (such as stars) on the basis of a plurality of image data and generate a simulation image (hereinafter, referred to as a “trail simulation image”) of trails of the detected heavenly bodies is considered. According to this method, predicted trails of the stars after completion of shooting can be known by only the image pickup apparatus, without using a special external apparatus.
However, when the noise reduction process as described in Japanese Laid-Open Patent Publication (kokai) No. 2015-35717 is further executed to suppress the image quality from being degraded due to the fixed pattern noise, shooting of the black image needs to be performed in addition to shooting of images used for an computation to predict the movements of the stars. In this case, a long time is necessary to generate the trail simulation image, which results in degrading usability.